Please Note: This page is particularly important for understanding how the frequencies of cellular systems work and how the carriers use these frequencies. It also provides a good overview of how cellular systems are structured. Please read carefully and thoroughly, we think you'll learn a lot!

Bands and Frequencies

There are only two systems in the US in use in today's cellular system. Regardless of the terminology (aka; Modes) used to characterize cellular technology (PCS, TDMA, CDMA, GSM, GPRS, Cellular, Digital, Analog, etc.), at this time there are only two frequency ranges (aka; Bands) available to US carriers. ( Nextel users go here )

(1) 824-896 MHz commonly termed 800 MegaHertz (may also be known as 850MHz)

(2) 1850MHz-1990MHz commonly termed 1900 MegaHertz or 1.9 GigaHertz

For simplicity's sake we will stick to the terms 800 MegaHertz and 1900 MegaHertz . MegaHertz is abbreviated as MHz .

Some cellular carriers are using only one of these frequency ranges and many use both . To utilize both frequency ranges they have contracted with the cellular phone manufacturers to design phones that are capable of these two bands . This is where the term "Dual Band" comes from. As an example, the Nokia 6160 is a Dual Band Phone . (Note: remember that the frequencies are also known as bands )

Dual Band - Tri Mode and Tri-Band Phones

Before we go too far, it must be further explained that the frequencies(bands) that your phone can use have nothing to do with the Modes . Modes refers to the technology being used in those frequencies. These modes include Analog, Digital, TDMA, CDMA, GSM, etc. The modes of a cellular phone do not effect the antennas that your phone can use as all antennas are tuned to frequencies(bands) and not modes . The actual definition of a Dual Band-Tri Mode Phone - 800MHz Analog, 800MHz Digital and 1900MHz Digital. Two Bands and Three Modes .

New Tri-Band Phones utilize 900MHz, 1800MHz and 1900MHz frequencies. Seems like you're getting quite a GREAT deal, Right? Afterall, you have a Tri-Band and not just a Dual-Band Phone. The truth: the first two frequency ranges are NOT used here in the US. In reality you have a single band phone using 1900MHz here in the US. The other frquencies are used outside the US.

That said, it is particularly important that you obtain the correct frequency antenna for use for your application. since the cell site is looking for a phone sending on the frequency range it is sending out.

Notice how the cell site (A) sends out in the specified frequency range and the appropriate phones send back in that same frequency range.

This is particularly important for fixed applications such as a home or office. The frequency range that your phone uses in your home or office does not change . If you are travelling around in your car and moving from city to city, a dual band phone may switch to the other frequency range(band) without you even noticing it. The cellular system and your Dual Band phone were designed to make this switch (handoff, see below) seamlessly. There is NO indication to the user exactly which frequency you are using.

For mobile applications (and some fixed) a dual band antenna should be used to ensure that you have both frequency ranges(bands) available to your phone. However, if you select for example a 1900MHz antenna for your home area and you roam to another system which is 800MHz your phone will get NO reception while hooked up to an external antenna. A Dual Band antenna for mobile applications is the best and most common selection.

How the Cellular System Works

Let's look at frequencies from a different perspective. Each Carrier (AT&T, Verizon, Sprint, etc.) uses their own (no sharing!) cell sites. If you are in one location, chances are you are being blanketed by three or four carriers even though you are only concerned with one. Take a look at this example:

Let's just say you have a phone and plan that works with Carrier 4 . Your phone, from where you are, is in the carrier's cell (purple area) site using 800MHz. The cell site is to the east of you. Can you use the cell sites of the other carriers? NO , more than likely your phone is not compatible and you do not have a contract (service) with the others. However, if your friend visits you and he has a phone with service from Carrier 1 , he will get good reception though he will be on his carrier's cell site to the west . This is particularly important to understand when looking at fixed application antennas.

Let's get back to your Carrier #4 . Take a look at this illustration:

Here we have removed all of the other carriers to show the system that your phone uses, Carrier 4 .

Notice that with a dual band phone you can move from Point A (Cell Site 1) using 1900MHz to Point B (Cell Site 2) still using 1900MHz and then on to Point C (Cell Site 3) where your phone has switched to 800MHz . However, if you are using your phone in a fixed location, say within the area of Cell Site 4, you would ALWAYS be using 800MHz and it would never change unless the carrier changes it (VERY RARE) or you change carriers, equipment and change your mobile number. As an aside, we could make three more illustrations just like the one above. Each carrier's illustration would overlay the other carrier's system. So for round figures, we could say that if there are four carriers and to cover the above area takes four cell sites, you could probably locate 16 cell sites covering this area. Remember, each carrier uses their own cell sites to comprise their system. So if you had a master map you could identify the location of each cell site and who it belongs to. This information is VERY DIFFICULT to come by. The carriers are VERY protective of this information due to competition.

As another aside--Notice how each Cell Site covers a specific area and is at a specific frequency range. These areas are known as Cells . This is where the term Cellular comes from. See how the cells do not overlap by much at all. This is done to maximize coverage for the specific area without wasting signal for areas already covered. The cell sites use sophisticated switching equipment to transfer your phone call from one cell site to the next. This is called a handoff . As you get too far from one cell site and the call quality becomes unacceptable, the cellular system looks for the next cell site and frequency to hand your call off to. All of this happens in split seconds and is not obvious to the user.